I did notice this along with a couple of other things (I have a 2011 Macbook air with 4GB RAM). The memory pressure turned yellow earlier than I remembered with 10.10.2 and my memory used has been quite a bit lower since upgrading to 10.10.3. I used to be just after a fresh reboot without launching anything I would have around 500MB of free memory and now it's over a gig and stays around there even if I'm web browsing.